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What is Liquid Penetrant Testing?

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  • Written By: B. Turner
  • Edited By: Bronwyn Harris
  • Last Modified Date: 09 June 2018
  • Copyright Protected:
    2003-2018
    Conjecture Corporation
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Liquid penetrant testing is a process used for testing and inspecting various objects for defects or flaws. It is a non-destructive type of testing process, which means that the object is not damaged or destroyed as it is tested. Many manufacturing and industrial facilities rely on liquid penetrant testing to confirm the safety and quality of their products.

During liquid penetrant testing, a dye is applied to the surface of an object. Through a process known as "capillary action," the dye quickly penetrates any flaws or cracks in the object's exterior. After a pre-determined period of time, the object is wiped clean, and all surface dye is removed. A developing powder is applied, which helps to brighten or expose any remaining dye that has settled into surface cracks or voids. The remaining dye indicates the location of any flaws or defects that must be corrected on the object.

There are two basic varieties of liquid penetrant testing used by manufacturers and inspectors. The first uses a visible, colored dye to indicate flaws, while the other relies on a fluorescent dye that is invisible to the naked eye. When the fluorescent dye is used, inspectors must examine the object under an ultraviolet (UV) light to view defects.

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Liquid penetrant testing may be used on both metal and nonmetal objects, including ceramic, plastic and even glass. It is commonly used in manufacturing plants, to test things like cars, aeronautical equipment, machinery and consumer items. Nondestructive liquid penetrant testing is also an excellent method of inspecting building components without damaging or destroying the object during the process.

This testing process helps to reveal defects such as cracks, holes or voids that may not be detected using visual or other inspection procedures. Liquid penetrant surface testing can also detect welding flaws in the seam between two different items. Finally, this test can be used to detect corrosion or other chemical processes that may have compromised the structural integrity of the object.

Liquid penentrant testing is known for its relatively low cost, especially compared to other materials testing techniques. The process is easy to perform, and results are available quickly. Even inspectors who are relatively new to this testing process can easily interpret the results of this test in most cases.

While this test offers many benefits to users, it also has a number of limitations that must be considered. Liquid penetrant testing is only designed to find flaws on the surface of an object, and will not detect problems deep below the surface. In addition, the surface of an object must be relatively smooth and free of dirt, grease and other substances that can skew the results of the test.

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